In the 1970s, the International Socialists (IS) oriented on the restive US working class in industries like Auto and Teamsters in an effort to organize rank and file movements that, they hoped, would position them to build a “workers’ combat organization" in the US. In the Spring of 1977, a small group of about 75 revolutionaries constituted themselves as the International Socialist Organization (ISO) and launched a monthly newspaper, Socialist Worker. They had been members of the “Left Faction” of the IS, but were expelled in 1977 after expressing disagreements with the IS’s industrialization and “mass work” perspectives, which, they believed, were leading it in the wrong direction. This talk will explore the origins of the ISO and the struggles and debates that shaped this period, drawing lessons for socialists today.